We propose to investigate the reciprocity between the behavioral and thermoregulatory properties of the ocular Harderian gland in Meriones unguiculatus. Our investigations indicate that the gland secretes lipids and pigments to the nares of the nose during thermoregulatory autogrooming. The material is spread copiously on the face and fur and can be seen with ultraviolet light stimulation. The Harderian material attracts conspecifics and insulates the body against low ambient temperatures and wetness. The chemosignal is rapidly degraded by the saliva associated with the groom. These are the first unambiguous functions ascribed to the gland since its discovery in 1694, and may be of great significance for the behavioral adaptation of most mammalian species. This proposal extends these observations in several dimensions: (1) the clarification of the release mechanism for Harderian secretion during thermoregulatory autogrooming and the elucidation of the Harderian tract system, (2) detailing of the longevity of the Harderian chemosensory properties and their relationship to salivary degradation of the signal, (3) investigation of a wide range of social interactions affected by Harderian material, including induction of grooming in conspecifics, nose-to-nose investigations, aggression, and sandbathing, (4) parsing of physiological and behavioral consequences of Harderianectomy, with emphases on body temperature reactions to heat and cold, oxygen consumption and evaporative water loss, and (5) the study of heat absorption and behavioral adaptations related to the loss of hair pigments following Harderian gland removal or sandbathing. These studies will clarify the reciprocal interaction of behavior and Harderian secretion and establish links between chemosignaling and thermoenergetics. They will also provide insights into the associations between Harderian secretion and other forms of communication in M. unguiculatus, such as ventral scent marking and ultrasounding.